Thermally tunable optical dispersion compensation devices

ABSTRACT

Optical dispersion compensation (ODC) devices are disclosed. In one aspect, an ODC device may include first and second groups of optical resonator devices coupled together to compensate for optical dispersion by collectively delaying light. The first group of optical resonator devices may have a first group delay curve with a convex shape between peaks in frequency. The second group of optical resonator devices may have a second group delay curve with a concave shape at a peak in frequency. The ODC device may also include one or more thermal devices to change the temperature of the first group of optical resonator devices as a group, and one or more additional thermal devices to change the temperature of the second group of optical resonator devices as a group. Methods of making and using the ODC devices are also disclosed, as well as various systems including the ODC devices.

CROSS-REFERENCE TO RELATED APPLICATION

The present application cross-references the application entitled“THERMALLY TUNABLE OPTICAL DISPERSION COMPENSATION DEVICES,” filed onMar. 31, 2006, assigned U.S. patent application Ser. No. 11/395,887, andpatented on Jul. 22, 2008, assigned U.S. Pat. No. 7,403,679.

BACKGROUND

1. Field

Embodiments of the invention relate to the field of opticalcommunications. In particular, one or more embodiments of the inventionrelate to optical dispersion compensation.

2. Background Information

Optical dispersion may occur in optical fiber and other opticalmaterials. A common source of dispersion in optical fibers is chromaticdispersion (CD).

Chromatic dispersion may occur due to the speed of light being dependenton the refractive index of the medium within which the light ispropagating. In many materials that may be used for optical fibers, therefractive index may vary with the wavelength of the light. As a result,light with different wavelengths may be transmitted through the opticalfiber at slightly different speeds. This may result in the differentwavelengths of light of a transmitted pulse to spread out or disperseover time and length of transmission. Such dispersion is generallyundesirable.

Various approaches for reducing optical dispersion in fibers are knownin the arts. One approach includes using a dispersion compensatingfiber. However, dispersion compensating fibers may tend to costly orhave increased optical loss. Another approach includes using electronicdispersion compensation. However, there are known disadvantagesassociated with electronic dispersion compensation, such as, forexample, in some cases physical size or power consumption.

Optical dispersion compensation is yet another approach that may beused.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1 is a block diagram of an optical receiver including an opticaldispersion compensation (ODC) device, according to one or moreembodiments of the invention.

FIG. 2A is a block diagram of a cross-sectional view of a G-T etalon,according to one or more embodiments of the invention.

FIG. 2B is an exemplary plot of delay versus frequency for an exampleG-T etalon.

FIG. 3 is a block diagram of an ODC device, according to one or moreembodiments of the invention.

FIG. 4 is a plot showing how the ODC device of FIG. 3 may compensate foroptical dispersion, according to one or more embodiments of theinvention.

FIG. 5 is a plot showing that the amount of optical dispersioncompensation may vary from one implementation to another.

FIG. 6A is a block diagram of a cross-sectional view of a G-T etalonhaving a temperature dependent reflectivity, according to one or moreembodiments of the invention.

FIG. 6B is a top planar block diagram view of an ODC device includingring resonators microfabricated on a substrate, according to one or moreembodiments of the invention.

FIGS. 7A-B are plots showing how an ODC device similar to that shown inFIG. 3 having etalons similar to those shown in FIG. 6A with temperaturedependent partial reflectors may compensate for varying amounts ofoptical dispersion, according to one or more embodiments of theinvention.

FIG. 8A is a block diagram of an ODC device, according to one or moreembodiments of the invention.

FIG. 8B is a top planar block diagram view of an ODC device includingfirst and second groups of optical ring resonators microfabricated on asubstrate, according to one or more embodiments of the invention.

FIG. 9 is a block diagram of a top planar view of an ODC device coupledwith a substrate, according to one or more embodiments of the invention.

FIG. 10A is a plot showing delay curves for a positive curve group ofetalons, according to one or more embodiments of the invention.

FIG. 10B is a plot showing delay curves for a negative curve group ofetalons, according to one or more embodiments of the invention.

FIGS. 11A-E are plots showing how the positive and negative curves shownin FIGS. 10A-B may be added together for different temperatures for thegroups to provide varying levels of optical dispersion correction,according to various embodiments of the invention.

FIG. 12 shows a temperature control and temperature-sensingconfiguration for one or more etalons, according to one or moreembodiments of the invention.

FIG. 13 is a perspective view of a G-T etalon having an integratedresistive heater and an integrated temperature sensor, according to oneor more embodiments of the invention.

FIG. 14 is a block diagram of a top planar view of an optical receiverpackage, according to one or more embodiments of the invention.

FIG. 15 is a block diagram of an optical transceiver, according to oneor more embodiments of the invention.

FIG. 16 is a block diagram of network equipment including an opticaltransceiver including an ODC device, according to one or moreembodiments of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description.

I. Optical Receiver Having ODC Device

FIG. 1 is a block diagram of an optical receiver 100 including anoptical dispersion compensation (ODC) device 102, according to one ormore embodiments of the invention. The optical receiver also includes alight detector device 104, a reception processing logic 106, and controllogic 108.

Dispersed light 110, for example due in part to chromatic dispersion,may be input to the ODC device. By way of example, the ODC device may becapable of being optically coupled with an optical fiber, embeddedwaveguide, or other source of the dispersed light. The ODC device mayoptically compensate for or reduce the amount of dispersion of thelight. As used herein, compensating for optical dispersion does notrequire full compensation or compensating to any level but merelyreducing optical dispersion by a sufficient amount for the particularimplementation. Various ODC device embodiments will be discussed infurther detail below. The ODC device may provide dispersion compensatedlight 112 having reduced dispersion as output.

The light detector device may be optically coupled with the output ofthe ODC device and may receive the dispersion compensated light. Thelight detector device may detect the received dispersion compensatedlight. The light detector device may convert the received light to acorresponding output electrical signal 114, such as, for example, anelectrical current. Examples of suitable light detector devices include,but are not limited to, indium phosphide (InP) and gallium arsenide(GaAs) PIN (Positive-Intrinsic-Negative doped structure) photodiodes,and InP avalanche photodiodes (APD), although the scope of the inventionis not limited to just these particular light detector devices.

The reception processing logic may be electrically coupled with theoutput of the light detector device. The reception processing logic mayinclude hardware, such as, for example, a circuit, software, firmware,or a combination thereof. The reception processing logic may processesthe electrical signals corresponding to the received dispersioncompensated light. By way of example, the reception processing logic mayinclude a DMUX/CDR (Demultiplexer/Clock Data Recovery) circuit. TheDMUX/CDR circuit may include a demultiplexer with built in CDR circuit.However, the scope of the invention is not limited to this particulartype of reception logic. In one or more embodiments of the invention,the logic may include error correction logic to correct errors in thereceived data. In one or more embodiments of the invention, the errorcorrection logic may generate an error metric, such as, for example, abit error rate (BER) corresponding to the previously dispersioncompensated signals, and may provide the error metric to the controllogic.

The control logic may be coupled with the reception processing logic andthe ODC device. In one or more embodiments of the invention, the controllogic may receive the BER or other error metric from the receptionprocessing logic, and may tune, or control, or otherwise adjust the ODCdevice based, at least in part, on the BER or other error metric. In oneor more embodiments of the invention, a feedback loop may be used totune or otherwise adjust the ODC device based on the error metric inorder to adjust the amount of optical dispersion compensation, althoughthis is not required. A high BER may indicate that the device may not beoptimally tuned, and tuning may accordingly be performed to better tunethe device and reduce the BER. In one or more embodiments of theinvention, tuning the ODC device may include controlling one or moretemperatures of the ODC device in order to provide an optical dispersioncompensation having particular characteristics. The ODC device may alsoor alternatively optionally be controlled based on other information.Such auto tuning or adjustment may potentially be advantageous incertain implementations, such as, for example, in add-drop networkswhere the transmission distance of the received optical signal may beunknown, or where the amount of introduced optical dispersion may beotherwise variable or unknown.

II. Introduction to Etalons

In one or more embodiments of the invention, etalons may be used foroptical dispersion compensation, although the scope of the invention isnot limited in this respect. An etalon may include an optical devicehaving two or more generally flat, parallel, reflecting surfaces. Thereflecting surfaces may be located at opposite ends of an optical cavitythat may include a transparent solid, gas, or vacuum. Light may reflectback and forth between the reflective surfaces. Resonance may occur inthe etalon at certain frequencies based on interference of light, whichmay depend upon the thickness of and optical properties of the cavity.The etalon may be used for optical compensation.

One example of a suitable type of etalon is a Gires-Tournois (G-T)etalon, although the scope of the invention is not limited to G-Tetalons. G-T etalons are a type of optical all-pass resonant filter.Other types of all pass resonant filters may also optionally be employedin alternate embodiments of the invention. FIG. 2A is a block diagram ofa cross-sectional view of a G-T etalon 216, according to one or moreembodiments of the invention. The G-T etalon includes two or morereflectors 218, 220 separated by an optical cavity 222. In particular,the G-T etalon includes a partial reflector 218 and a high reflector 220on opposite sides of the optical cavity.

The partial reflector has a significantly lower reflectance than thehigh reflector. By way of example, the partial reflector may have areflectance in the range of about 10 to 70%, or about 20 to 60%, forexample, and the high reflector may have a reflectance that may begreater than 90%, or may be greater than 95%, or may be greater than99%, depending upon the particular implementation. For clarity, as usedherein, a “partial reflector” has a reflectivity that is less than 70%,and a “high reflector” has a reflectivity that is greater than 90%”. Thereflectivity of the high reflector may approach total reflectivity.

By way of example, the reflectors may include one or more reflectivesurfaces. Suitable reflective surfaces include, but are not limited to,those provided by reflective single layers, such as, for example highlyreflective metal layers, and those provided by stacked layers, such as,for example, dielectric stacks. Suitable highly reflective metal layersinclude, but are not limited to, gold and silver layers. The dielectricstacks may include multiple layers of materials that have differentindexes of refraction. In one particular embodiment of the invention,the high reflector may be a gold layer, and the partial reflector may bea dielectric stack of silicon and silicon dioxide, although the scope ofthe invention is not so limited.

The optical cavity may be disposed between the reflectors. The opticalcavity may include a solid, a gas, or a vacuum. In one or moreembodiments of the invention, the optical cavity may include crystallinesilicon, such as, for example, single crystal silicon, although thescope of the invention is not limited in this respect. The use ofcrystalline silicon may offer certain potential advantages in someimplementations, which will be explained in further detail below.

Light may be delayed in a G-T etalon when a frequency of incident lightis near a resonance frequency of the G-T etalon. The resonant frequencymay occur when the optical path length is around (q)(lambda)/2, where qis an integer, and lambda represents the wavelength of light measuredinside the etalon material.

FIG. 2B shows a plot of delay versus frequency for an example G-Tetalon. Two delay curves are shown. As shown, each of the delay curveshas a shape that is substantially Lorentzian. Each of the delay curveshas a peak or maximum delay. As shown, the delay due to a G-T etalon maybe a function of frequency. In one or more embodiments of the invention,such delay may be used to compensate for optical dispersion.

The full-width half max (FWHM) of the etalon measures the width of acurve. The FWHM may be largely based on the partial reflectivity of theetalon.

The free spectral range (FSR) of a G-T etalon represents the distance infrequency space between adjacent peaks. The FSR may be based on theoptical path length through the optical cavity, or the spacing betweenthe reflectors, and the index of refraction of the optical cavity. TheFSR of a G-T etalon may be adjusted by adjusting the spacing between thereflectors, the index of refraction of the optical cavity, or both. Eachresonant mode of the etalon may occur at an integer multiple of a halfwavelength. In certain optical communication protocols channels may bespaced apart by an FSR of about 50 GHz. By way of example, a 3 mmoptical path length of air or a 1 mm optical path length of silicon mayprovide such a 50 GHz FSR.

Etalons may be optically tuned or adjusted by tuning or adjusting theirtemperature. The change in temperature may result in a correspondingchange in material thickness, material refractive index, or somecombination. If the temperature change is sufficient, a peak or maximumdelay may be translated in the frequency domain one full period or mode.

In one or more embodiments of the invention, change in temperature mayalso change reflectivity. Accordingly, thermal tuning may be used tochange FWHM of etalons.

III. First Exemplary ODC Device Design

In one or more embodiments of the invention, a delay provided by a G-Tetalon may be used to compensate for or reduce optical dispersion. FIG.3 is a block diagram of an ODC device 302, according to one or moreembodiments of the invention. The ODC device includes two or more (aplurality) of etalons 316A-D optically coupled together, such as, forexample, in series. The etalons may compensate for optical dispersion bycollectively delaying light. In one or more embodiments of theinvention, the etalons may include G-T etalons, although the scope ofthe invention is not limited in this respect.

In particular, the illustrated ODC device includes a first G-T etalon316A, a second G-T etalon 316B, a third G-T etalon 316C, and a fourthG-T etalon 316D, although the scope of the invention is not limited inthis respect. In alternate embodiments of the invention either fewer ormore etalons may optionally be included. The etalons may optionally havesome or all of the characteristics of the etalons discussed elsewhereherein. For brevity, and to avoid obscuring the description, thediscussion tends to emphasize different and/or additionalcharacteristics.

The first G-T etalon has a first partial reflector 318A, the second G-Tetalon has a second partial reflector 318B, the third G-T etalon has athird partial reflector 318C, and the fourth G-T etalon has a fourthpartial reflector 318D. In one or more embodiments of the invention, thepartial reflectors of the etalons may all have different reflectivities,although this is not required. The reflectivities of the etalons may bemade different by using reflectors having different materials,thicknesses, or numbers of stacked layers, for example. The differentreflectivities may give the etalons different delay response curvescharacterized by different peak delays and different FWHM. That is, theetalons may all have different FWHM and different peak delays, althoughthis is not required. As will be explained in further detail below, thedifferent FWHM and different peak delays may help to allow the sum ofthe delays of the etalons to approximate a linear delay response infrequency domain.

The ODC device also includes one or more thermal devices or temperaturecontrol devices (not shown). In one or more embodiments of theinvention, one or more or each of the etalons may be separately cooledand/or heated. For example, one or more separate dedicated thermaldevices or temperature control devices, such as, for example, athermoelectric controller (TEC), resistive heater, and/or thermoelectriccooler, may be included for one or more or each of the etalons. This mayallow the etalons to be cooled and/or heated to different temperatures.Alternatively, two or more or all of the etalons may be cooled and/orheated to the same or similar temperature with a common heating and/orcooling device. In one or more embodiments of the invention, one or moreor all of the reflectivities of the etalons may be temperaturedependent, although this is not required. As will be explained infurther detail below, the temperature dependent reflectivities may allowfor different amounts of dispersion to be compensated for.

Other aspects of the design of the etalons, such as, for example, thehigh reflectors and the optical cavity thicknesses, may optionally bethe same or similar, although the scope of the invention is not limitedin this respect. This may potentially help to simplify fabrication.

IV. Plot Showing Compensation for Optical Dispersion with FirstExemplary ODC Device Design

FIG. 4 is a plot showing how the ODC device of FIG. 3 may compensate foroptical dispersion, according to one or more embodiments of theinvention. The plot shows delay in picoseconds (ps) plotted on they-axis against frequency in gigahertz (GHz) on the x-axis.

A straight line (labeled “line”) represents the amount of opticaldispersion compensation that would undo the amount of optical dispersionintroduced by an optical fiber. In some optical fibers, the amount ofoptical dispersion introduced varies approximately linearly withfrequency of light. The particular illustrated straight line has anoptical dispersion slope of about 2000 ps/nm and may be sufficient torepresent the amount of optical dispersion for particular opticalfibers, but not all optical fibers.

Four different delay curves labeled 1, 2, 3, and 4, each represent adelay versus frequency response curve for a different one of the fourG-T etalons. The shapes of the delay curves are substantiallyLorentzian. A smaller FWHM may tend to lead to a higher peak delay. Asshown, each of the curves has a different center frequency or peak ormaximum delay. That is, the center frequencies or peaks of the fourdifferent delay curves are shifted in frequency. In one or moreembodiments of the invention, the shift of the center frequency may bedue at least in part to a phase shift of light, such as, for example,due to a difference in thickness of a phase adjustment or spacer layerwhich may optionally be part of a reflective dielectric stack and whichmay help to adjust both reflection amplitude and phase to suitablevalues, although this is not required. The distance between the peaks ofthe two curves labeled “1” represents the FSR for the correspondingetalon.

A group delay curve (labeled “group delay curve”) representing the sumof the four different delay curves is also shown. As shown, the groupdelay curve has an approximately linear shape that closely approximatesthe straight line that is used to represent the expected level ofoptical dispersion in the optical fiber. The group delay curverepresents the combined effect of the four different G-T etalons and maybe used to compensate for or reduce the optical dispersion.

This is just one example. The scope of the invention is not limited tojust this one example. In alternate embodiments of the invention, theetalons may optionally be based on different bandwidths. For example,instead of a bandwidth of about 20 GHz, the etalons may be based on abandwidth of about 15 GHz, or a bandwidth of about 10 GHz, to name justa few examples. Simulations with 10, 15, and 20 GHz ODC devices seem toindicate that the group delay curve may more closely approximate thestraight line representing optical dispersion with decreasingbandwidths.

In still further alternate embodiments of the invention, differentnumbers of etalons may optionally be included in an ODC device. Forexample, instead of four etalons the ODC device may include five or sixetalons, to name just a few examples. Simulations with 4, 5, and 6etalon ODC devices seem to indicate that the group delay curve may moreclosely approximate the straight line representing optical dispersionwith increasing numbers of etalons.

V. Changing Dispersion Slope

FIG. 5 is a plot showing that the slope of the straight linerepresenting the amount of optical dispersion compensation that wouldundue the optical dispersion introduced by an optical fiber may varyfrom one implementation to another. The plot shows delay on the y-axisagainst frequency on the x-axis. Two straight lines are shown. Thedifferent straight lines have different slopes when plotted as delayversus frequency. The different slopes may represent different amountsof optical dispersion compensation to undue introduced opticaldispersion. The amount of introduced optical dispersion may vary due tovarious factors, such as, for example, differences in fiber material,condition of the fiber, whether or not dispersion compensating fiber isused, whether or not optical dispersion pre-compensation has beenperformed, and the like. In some cases, the slope may even beapproximately zero or even negative. Since the slope may vary, it may beadvantageous in some implementations to be able to adjust or tune an ODCdevice so that the group delay curve representing the combined delayresponse of the etalons may approximate lines having different slopes.This may help to allow a single ODC device to compensate for varioustypes of optical dispersion.

VI. Etalon Having Temperature Dependent Reflector

FIG. 6A is a block diagram of a cross-sectional view of a G-T etalon616, according to one or more embodiments of the invention. The G-Tetalon includes a temperature dependent partial reflector 618, a highreflector 620, and a thick optical cavity 622 disposed between thetemperature dependent partial reflector and the high reflector.

The temperature dependent partial reflector itself has a structuresomewhat similar to an etalon, such as, for example, a Fabry-Perot (F-P)etalon. In particular, the temperature dependent partial reflectorincludes a first, outer low or partial reflector 630, a second, innerlow or partial reflector 634, and a thin optical cavity 632 disposedbetween the first and second low reflectors.

In one or more embodiments of the invention, the inner, second lowreflector may have a reflectance that is greater than a reflectance ofthe outer, first low reflector. By way of example, and not limitation,the first low reflector may have a reflectance of about 5 to 15%, andthe second low reflector may have a reflectance of about 20 to 40%,although the scope of the invention is not limited in this respect. Eachof the low reflectors may include a single reflective layer or adielectric stack, for example.

The high reflector may likewise be a single reflective layer ordielectric stack. The high reflector may have a significantly greaterreflectance than the low reflectors. By way of example, the highreflector may have a reflectance of at least 90%, at least 95%, at least98%, or at least 99%.

The thin optical cavity may be thinner than, or otherwise have a shorteroptical path length than, the thick optical cavity. By way of example,and not limitation, the thick optical cavity may have an optical pathlength that gives a FSR of about 50 GHz, whereas the thin optical cavitymay have an optical path length that gives a FSR of about 275 GHz,although the scope of the invention is not so limited. Other FSR arealso suitable. In one or more embodiments of the invention, the opticalpath length of the thinner optical cavity is less than half the opticalthickness of the thicker optical cavity, although the scope of theinvention is not so limited.

In one or more embodiments of the invention, one or more or each of thethin and thick optical cavities may include crystalline silicon, galliumarsenide, or another high index material, although the scope of theinvention is not limited in this respect. Semiconductor materials suchas silicon and gallium arsenide provide a relatively large change inrefractive index with temperature and may optionally be used in theoptical cavities for enhanced tuning over a relatively small range oftemperature. By way of example, single crystal silicon has athermo-optic coefficient of about 10 GHz/° C., compared to about 1 GHz/°C. for fused silica. This may allow a larger tuning range to beaddressed using a smaller temperature range. For example, single crystalsilicon may offer significant tuning over a relatively small temperaturerange of about 30° C. Significantly larger temperature ranges may beneeded to achieve the same or similar tuning for materials such as fusedsilica. These larger temperature ranges may have drawbacks, such as, forexample, increased power consumption, undesirable convective effects,and decreased reliability when components are heated and cooledrepeatedly over a large range, etc. Traditionally, crystalline siliconis not commonly used in optical elements because it tends to bethermally sensitive and tends to absorb at commonly encounteredwavelengths.

The thicker optical cavity may behave substantially like a G-T etalonwith a high reflector and a low reflector having an effectivereflectivity based on the composite reflectivity of the thinneroverlying optical cavity. The temperature dependent partial reflectormay be considered a Fabry-Perot (F-P) etalon. In one or more embodimentsof the invention the temperature dependent partial reflector has atemperature dependent reflectivity of at least 0.01%/° C., although thescope of the invention is not so limited. The composite reflectivity ofthe F-P etalon may not be constant with wavelength, but may varyperiodically with a period approximately equal to the FSR of the F-Pcavity. This composite reflectivity F-P cavity may be thermally tuned ina manner analogous to the thermal tuning of a G-T etalon considered inisolation.

When the G-T etalon is optically coupled to the F-P cavity as shown anddescribed here, the thermal tuning of the resulting coupled structuremay be interpreted as thermal tuning of a G-T etalon where thereflectivity of the partial reflector is temperature dependent and maybe thermally tuned to various different partial reflectivities. A methodmay include changing a temperature of the etalon to change thereflectivity of the partial reflector. Without limitation, to furtherillustrate certain concepts, let's consider a concrete example of anetalon having a structure similar to that shown in FIG. 6A. The thickerG-T cavity may have a FSR of about 50 GHz, the thinner F-P cavity mayhave an FSR of about 275 GHz, and these cavities may be fabricated fromsingle crystal silicon, which has a thermo-optic coefficient of about 10GHz/° C. If one observes the group delay peak at a particular wavelengthas this etalon is heated, a succession of group delay peaks may sweeppast the particular wavelength, with the peaks corresponding to the G-Tetalon and spaced approximately every 5° C. Since the G-T cavity has aFSR of 50 GHz and a tuning rate of 10 GHz/° C., about 5° C. is thetemperature spacing between the G-T cavity resonances. These peaks donot have identical FWHM. Rather, the FWHM may be based on thetemperature dependent reflectivity of the F-P cavity at that particulartemperature and wavelength, such that changing the temperature mayinclude changing the FWHM. The F-P cavity may have resonances aboutevery 275 GHz, corresponding to a thermal period of about 27.5° C. Thereflectivity of the F-P cavity may vary relatively smoothly over thisthermal period as the cavity is tuned out of resonance and thenre-approaches the next resonance at about 27.5° C. intervals. From theG-T cavities viewpoint, the reflectivity sampled at about each 50 GHzresonance, which may be addressed by a 5° C. temperature change, may setthe peak group delay of that resonance. Accordingly, there may bethermal tuning of the reflectivity in combination with the ability tothermally address the etalon's tuning period many times over. This mayallow both the center frequency and the dispersion slope of the ODCdevice to be tuned. The scope of the invention is not limited to thisparticular example.

Now, other approaches for achieving temperature dependent reflectivitiesare also contemplated, such as, for example, using a dielectric stackwith a thick layer of a high thermo-optic coefficient material, such as,for example, single crystal silicon. In one or more embodiments of theinvention, the thick layer of the high thermo-optic coefficient materialmay have a thickness of at least 0.5 microns. The thick layer may beformed by deposition or polishing, for example. Other temperaturedependent partial reflectors known in the arts are also potentiallysuitable.

Now, the use of G-T etalons is not required. In one or more embodimentsof the invention, optical rings may be used in place of G-T etalons todelay light and compensate for optical dispersion. The optical pathlength around the ring may be roughly analogous to the optical pathlength through the optical cavity of a G-T etalon. Likewise, theeffective coupling coefficient of a ring to a waveguide may be roughlyanalogous to a partial reflectivity of a G-T etalon.

FIG. 6B is a top planar block diagram view of an ODC device 602including ring resonators 615A-B, 617A-B microfabricated on a substrate644, according to one or more embodiments of the invention. An embeddedwaveguide 613 is microfabricated in or on the substrate. Two pairs ofoptical rings are also microfabricated in the substrate, although feweror more pairs of optical rings may optionally be included in alternateembodiments. The term ring does not imply circular and the rings mayoptionally be oval or otherwise non-circular.

A first pair includes a first smaller ring 617A and a first larger ring615A. A second pair includes a second smaller ring 617B and a secondlarger ring 615B. Each of the smaller rings may be evanescently orotherwise optically coupled with the waveguide, and the rings withineach of the pairs may be evanescently or otherwise optically coupledtogether. The amount of optical coupling may be based at least in parton separation distance, and may also be based at least in part on acoupling length. Generally, the smaller the separation distance and thelarger the coupling length, the greater the optical coupling.

In one or more embodiments of the invention, the smaller optical ringsmay be optically coupled to the waveguide with different amounts ofoptical coupling. For example, in one or more embodiments of theinvention, different separation distances and/or different couplinglengths may be used for the smaller optical rings. By way of example, asshown in the illustrated embodiment, one or more of the optical ringsmay be elongated or oval in the direction of the waveguide in order toincrease the coupling length with the waveguide.

The smaller rings may provide temperature dependent effective couplingcoefficients to their corresponding larger rings. These differenteffective coupling coefficients may be used in roughly an analogous wayas temperature dependent partial reflectivities to compensate fordifferent amounts of optical dispersion.

The illustrated ODC device includes an optional first monolithicallyintegrated temperature sensor 693A for the first pair of rings, and anoptional second monolithically integrated temperature sensor 693B forthe second pair of rings. The illustrated ODC device also includes anoptional first monolithically integrated temperature control device694A, such as, for example, a resistive heater, for the first pair ofrings, and an optional second monolithically integrated temperaturecontrol device 694B for the second pair of rings. As shown, thetemperature sensors and temperature control devices may optionally befabricated in close proximity of the rings, and may optionally conformin shape to the rings. As shown, an optional thermal insulator 692, suchas, for example, an inorganic or organic insulator, may be disposedbetween the pairs of rings to thermally insulate the pairs of rings fromone another.

VII. Plots Showing Compensation for Optical Dispersion with DifferentDispersion Slopes with First Exemplary ODC Device Design

FIGS. 7A-B are plots showing how an ODC device similar to that shown inFIG. 3 having one or more etalons similar to those shown in FIG. 6A withtemperature dependent partial reflectivities may compensate for varyingamounts of optical dispersion, according to one or more embodiments ofthe invention. The plots show that an ODC device may be tuned so thatgroup delay curves approximate different lines having different slopesto represent the expected different amounts of optical dispersions thatmay occur in optical fibers. In the plot on the left the group delaycurve approximates a line having a slope of about 2000 ps/nm, whereas inthe plot on the right the group delay curve approximates a line having aslope of about 1000 ps/nm. The variable reflectivity allows the FWHM,peak group delay, and wavelength where the peak delay occurs to bevaried for etalons so that a different set of curves may be used toachieve a 1000 ps/nm slope than were used for 2000 ps/nm. By way ofexample, but not limitation, the set of curves for the 1000 ps/nm slopemay have smaller peak delays and correspondingly wider FWHM. Not onlythese but a large number of gradually varying different slopes may beachieved by thermally tuning the etalons over the cyclic period whichfor silicon optical cavities is about 30° C. The temperatures thatachieve a suitable slope may be estimated through simulation andcalibrated for an actual device.

VIII. Second Exemplary ODC Device Design

FIG. 8A is a block diagram of an ODC device 802, according to one ormore embodiments of the invention. The ODC device includes a firstso-called “positive curve” group 840 of same or similar thicknessetalons that are heated to substantially the same or similartemperature, and a second so-called “negative curve” group 842 of sameor similar thickness etalons that are heated to substantially the sameor similar temperature. In one or more embodiments of the invention, theetalons may include G-T etalons, although the scope of the invention isnot limited in this respect.

The positive curve group includes a first etalon 816A, a second etalon816B, and a third etalon 816C. The negative curve group includes afourth etalon 816D, a fifth etalon 816E, a sixth etalon 816F, and aseventh etalon 816G. In alternate embodiments of the invention, fewer ormore etalons may optionally be included in either or both of the groups.It is not required that the groups have the same or similar number ofetalons. The etalons may optionally have some or all of thecharacteristics of the etalons discussed elsewhere herein. For brevity,and to avoid obscuring the description, the discussion tends toemphasize different and/or additional characteristics

The etalons of the positive and negative curve groups are opticallycoupled with one anther. In one or more embodiments of the invention,alternating etalons of the positive and negative curve groups areoptically coupled in series with one another, although this is notrequired.

The first etalon has a first partial reflector 818A, the second etalonhas a second partial reflectivity 818B, and the third etalon has a thirdpartial reflectivity 818C. Likewise, the fourth etalon has a fourthpartial reflectivity 818D, the fifth etalon has a fifth partialreflectivity 818E, the sixth etalon has a sixth partial reflectivity818F, and the seventh etalon has a seventh partial reflectivity 818G.

In one or more embodiments of the invention, etalons having a pluralityof different reflectivities and FWHM may be included within each of thepositive and negative curve groups. As discussed above, reflectivitiesmay be made different by using reflectors having different materials,different thicknesses, or different numbers of stacked layers, to namejust a few examples. Etalons with different reflectivities may havedifferent delay response curves characterized by different peak delaysand different FWHM. As will be explained in further detail below, in oneor more embodiments of the invention, the different reflectivities maybe selected to provide a group delay curve (the sum of the delay curvesof the etalons within a group) having a substantially parabolic shape,although the scope of the invention is not so limited.

In one or more embodiments of the invention, the etalons of the positivecurve group may be heated together to substantially the same or similartemperatures. Likewise, in such embodiments, the etalons of the negativecurve group may be heated together to substantially the same or similartemperatures. As used herein, unless specified otherwise, temperaturesof etalons are substantially the same when they are within 1° C. of oneanother. Controlling only two temperatures or less may offer certainadvantages in some embodiments over controlling more temperatures.Different approaches for heating the etalons will be discussed furtherbelow.

Other aspects of the design of the etalons, such as, for example, thehigh reflectors and the optical cavity thicknesses, may optionally bethe same or similar, although this is not required. This may potentiallyhelp to simplify fabrication. Alternatively, different high reflectorsand/or different optical cavity thickness may optionally be used.

A roughly analogous ODC device is contemplated in which optical ringresonators are used in place of G-T etalons. FIG. 8B is a top planarblock diagram view of an ODC device 802 including a first group ofoptical ring resonators 815A-C and a second group of optical ringresonators 815D-F microfabricated on a substrate 844, according to oneor more embodiments of the invention. Each of the optical rings of thefirst and second groups are optically coupled with an embedded waveguide813.

A first thermal device 850, such as, for example, a resistive heater,may optionally be microfabricated on the substrate or otherwisemonolithically integrated proximate the rings of the first group.Likewise, a second thermal device 852 may optionally be microfabricatedon the substrate or otherwise monolithically integrated proximate therings of the second group. Monolithically integrated temperature sensors(not shown) may optionally be similarly included, although this is notrequired. An insulating material 892 may optionally be disposed betweenthe rings of the first and second groups to provide improved thermalisolation, although this is not required.

IX. Concrete Example of Second Exemplary ODC Device Design

Referring again to ODC devices based on G-T etalons, FIG. 9 is a blockdiagram of a top planar view of an ODC device 902 coupled with asubstrate 944, according to one or more embodiments of the invention.The ODC device includes a first so-called “positive curve” group ofetalons 940 and a second so-called “negative curve” group of etalons942.

The positive curve group of etalons includes a first etalon 916A, asecond etalon 916B, and a third etalon 916C. The negative curve group ofetalons includes a fourth etalon 916D, a fifth etalon 916E, and sixthetalon 916F, and a seventh etalon 916G. As discussed, in alternateembodiments of the invention, fewer or more etalons may optionally beincluded in either or both of the groups. The groups may also optionallyhave the same or similar number of etalons.

In the illustrated embodiment, the etalons of the positive curve groupare monolithically fabricated on a single first monolithic substrate946. Likewise, the etalons of the negative curve group aremonolithically fabricated on a single second monolithic substrate 948.The etalon substrates are shown in cross-section and may bepick-and-placed or otherwise mounted or attached to the larger substrate944. Once mounted, the etalon substrates may be affixed with any epoxy,solder, or other adhesive. The etalon substrates may be batch fabricatedon one wafer and the larger package substrates may be batch fabricatedon a different wafer, although alternatively sets of each may befabricated together on a single wafer. As shown, the etalon substratesmay be aligned substantially parallel to one another so that the etalonsthereof are in reflective optical communication with one another. In oneor more embodiments of the invention, an optically flat spacer may beincluded between the etalon substrates to improve parallelism, althoughthis is not required. By way of example, the etalon substrates may havedimensions on the order of about one millimeter high by severalmillimeters wide, although the scope of the invention is not limited tothese particular dimensions. For simplicity and clarity of illustration,elements illustrated in the figures of the description have notnecessarily been drawn to scale. For example, the dimensions of some ofthe elements are exaggerated relative to other elements for emphasis orclarity. The devices shown herein may be used in other orientations thanthose illustrated.

The positive curve group of etalons share a first high reflector 920A,such as, for example, a highly reflective metal layer or dielectricstack, and the single first monolithic substrate, such as, for example,and a polished single crystal silicon substrate. Each etalon of thepositive curve group may have a different partial reflector. Inparticular, the first etalon has a first partial reflector 918A, thesecond etalon has a second partial reflector 918B, and the third etalonhas a third partial reflector 918C.

The negative curve group of etalons share a second high reflector 920B,such as, for example, a highly reflective metal layer or dielectricstack, and the single second monolithic substrate, such as, for example,and a polished single crystal silicon substrate. Each etalon of thenegative curve group may have a different partial reflector. Inparticular, the fourth etalon has a fourth partial reflector 918D, thefifth etalon has a fifth partial reflector 918E, the sixth etalon has asixth partial reflector 918F, and the seventh etalon has a seventhpartial reflector 918G.

In one or more embodiments of the invention, the first and thirdreflectors may optionally have the same or similar reflectivities and/orFWHM, the fourth and seventh reflectors may optionally have the same orsimilar reflectivities and/or FWHM, and the fifth and sixth reflectorsmay optionally have the same or similar reflectivities and/or FWHM. Thatis, within a group the reflectivities may be symmetrical about thecenter of the group. However, the scope of the invention is not limitedin this respect.

A method of fabricating a group of etalons, according to one or moreembodiments of the invention, may include polishing a monolithicsubstrate, forming a first high reflector on one side of the polishedsubstrate, and forming a plurality of partial reflectors on anotheropposite side of the polished substrate. A method of forming the partialreflectors, according to one or more embodiments of the invention, mayinclude depositing a resist layer, patterning the resist layer toprotect all but an intended location of deposition, depositing one ormore layers representing a partial reflector over the intended locationof deposition, removing the patterned resist layer, and repeating theoperations of depositing the resist, patterning the resist, anddepositing the one or more layers representing a partial reflector inorder to form the different partial reflectors. However, the scope ofthe invention is not limited to just this method.

The etalons of the positive and negative curve groups are opticallycoupled with one anther. As shown, the partial reflectors of thepositive curve group of etalons may be placed and aligned substantiallyfacing and parallel to the partial reflectors of the negative curvegroup of etalons. In the illustrated embodiment, alternating etalons ofthe positive and negative curve groups are optically coupled in serieswith one another, although this is not required.

Optically dispersed light from a source, such as, for example, anoptical fiber and/or collimating lens, may be impacted on the fourthpartial reflector of the fourth etalon. The forth etalon may reflect thelight to the first etalon. The first etalon may reflect the light to thefifth etalon, the fifth etalon may reflect the light to the secondetalon, the second etalon may reflect the light to the sixth etalon, thesixth etalon may reflect the light to the third etalon, the third etalonmay reflect the light to the seventh etalon, and the seventh etalon mayreflect the light to another destination, such as, for example, a lensand/or light detector device. The etalons may collectively performoptical dispersion compensation on the light so that the light reflectedby the seventh etalon may represent optical dispersion compensatedlight.

The positive curve group of etalons may be heated and/or cooled togetheras a group in a first heated region 950. Likewise, the negative curvegroup of etalons may be heated and/or cooled together as a group heatedregion 952. In this example configuration, one or more or each of thegroups may be separately thermo-optically tuned by separatelycontrolling the heating and/or cooling within the regions. To facilitatethermal isolation between the two regions, a thermal barrier orinsulator may be included between the regions. Examples of varioussuitable heaters, such as, for example, resistive heaters, will bediscussed in greater detail further below. In one or more alternateembodiments of the invention, coolers, such as, for example,thermo-electric coolers, may optionally be included for one or more ofthe groups, although this is not required. Passive cooling to ambient isanother option.

X. Plots Showing Positive and Negative Group Delay Curves

FIG. 10A is a plot showing delay curves for the so-called positive curvegroup of etalons, according to one or more embodiments of the invention.Three different delay curves labeled 1, 2, and 3 respectfully representa delay versus frequency response curve for the first, second, and thirdetalons of the positive curve group of etalons. As shown, each of thedifferent delay curves may have a different center frequency or peakdelay. That is, the center frequencies or peak delays of the threedifferent delay curves are shifted in frequency. In one or moreembodiments of the invention, the shift of the center frequency may bedue at least in part to a difference in thickness of a layer that may beused to adjust a phase of light, although this is not required. Otherapproaches for shifting the frequency are also potentially suitable. Asfurther shown, the curves for the first and third etalons havesubstantially similar shapes or FWHM and peak delays, although this isnot required. In the particular illustrated embodiment, the etalons havean FSR of about 20 GHz, although this is not required. A group delaycurve labeled “positive group” representing the sum of the threedifferent delay curves for the first, second, and third etalons of thepositive curve group of etalons is also shown. As shown, in one or moreembodiments of the invention, the group delay curve for the positivecurve group of etalons may have a substantially parabolic shape. Theparabola opens upward and is generally convex. The convex parabolicshape is between group delay peaks in the group delay curve, and has aminimum at a frequency of about 193500 GHz.

FIG. 10B is a plot showing delay curves for the so-called negative curvegroup of etalons, according to one or more embodiments of the invention.Four different delay curves labeled 4, 5, 6, and 7 respectfullyrepresent a delay versus frequency response curve for the fourth, fifth,sixth, and seventh etalons of the negative curve group of etalons. Asshown, each of the different delay curves may have a different centerfrequency or peak delay. That is, the center frequencies or peak delaysof the three different delay curves are shifted in frequency. In one ormore embodiments of the invention, the shift of the center frequency maybe due at least in part to a difference in thickness of a layer that maybe used to adjust a phase of light, although this is not required. Otherapproaches for shifting the frequency are also potentially suitable. Asfurther shown, the curves for the fourth and seventh etalons havesubstantially similar shapes, FWHM, and peak delays, although this isnot required. Likewise, the curves for the fifth and sixth etalons havesubstantially similar shapes, FWHM, and peak delays, although this isnot required. In the particular illustrated embodiment, the etalons havean FSR of about 100 GHz, although this is not required. By way ofexample, a crystalline silicon optical cavity thickness of about 0.4 mmmay provide this FSR. A group delay curve labeled “negative group”representing the sum of the four different delay curves for the fourth,fifth, sixth, and seventh etalons of the negative curve group of etalonsis also shown. As shown, in one or more embodiments of the invention,the group delay curve for the negative curve group of etalons may have asubstantially parabolic shape. The parabola opens downward and may begenerally concave. The concave parabolic shape is at group delay peaksin the group delay curve, and has a maximum at a frequency of about193500 GHz.

XI. Plots Showing Compensation for Optical Dispersion with DifferentDispersion Slopes with Second Exemplary ODC Device Design

In one or more embodiments of the invention, convex and concave groupdelay curves, such as, for example, parabolas, may be added together,superimposed, or otherwise combined in order to achieve a straight lineor other representation of an amount of optical dispersion compensationthat would undo the amount of optical dispersion introduced by anoptical fiber. As discussed above, at least to a first approximation, insome optical fibers, the amount of optical dispersion introduced variesapproximately linearly with frequency of light. Concave and convexparabolas may be added together or otherwise combined in order toprovide quite reasonable approximations to a straight line.

In one or more embodiments of the invention, the slopes of the lines maybe modified, or the ODC compensating characteristics of the ODC devicemodified, by adjusting the temperature of the positive curve group ofetalons, the negative curve group of etalons, or both. Adjusting thetemperature may include heating, cooling, or both heating and cooling.

For example, heating one group and cooling the other group by the sameor similar amount may change the slope without changing the centerwavelength. As another example, if all of the groups are heated by thesame or similar amount, the center wavelength may be changed withoutchanging the dispersion slope. As yet another example, heating one groupbut not all of the groups, may change the dispersion slope, and alsomove the center wavelength (frequency at which the peak delay occurs).

FIGS. 11A-E are plots showing how the positive and negative curves shownin FIGS. 10A-B may be added together for different temperatures for thegroups to provide varying levels of optical dispersion correction,according to various embodiments of the invention. FIG. 11A-Erespectfully show the positive and negative curves being added togetherto provide a line having a slope of about 6000 ps/nm, 3000 ps/nm, 0ps/nm (for example no substantive dispersion correction), −3000 ps/nm,and −6000 ps/nm. Accordingly, multiple group delay curves for multipledifferent groups of etalons may be added together to represent differentamounts and types of optical dispersion.

Each subsequent figure in the sequence going from A, to B, to C, to D,and then to E may differ from the preceding figure by tuning thepositive curve by about 2.5 GHz higher in frequency and tuning thenegative curve by about 2.5 GHz lower in frequency. For example and notlimitation, if the cavities of the positive curve group are fabricatedfrom single crystal silicon, which has a thermo-optic tuning rate ofabout 10 GHz/° C., then the positive curve group may be cooled by about0.25° C. to increase the frequency by about 2.5 GHz. If the cavities ofthe negative curve group are fabricated from crystalline silicon, thenthe negative curve group of etalons may be heated by about 0.25° C. todecrease the frequency by about 2.5 GHz.

Now, these are just a few examples. The scope of the invention is notlimited to just these particular examples. For example, rather thanlinear relationships, non-linear representations may also optionally berepresented or approximated by a combination of group delay curves. Asanother example, rather than just two group delay curves, three or moregroup delay curves may be combined. As yet another example, rather thanparabolic curves, curves having other shapes may optionally be used.Further modifications and adaptations will be apparent to those skilledin the art and having the benefit of the present disclosure.

XII. Exemplary Heaters and Temperature Sensors

FIG. 12 shows a temperature control and temperature sensingconfiguration for one or more etalons 1216, according to one or moreembodiments of the invention. The one or more etalons are mounted on asubstrate 1244. In one aspect, the one or more etalons may include asingle etalon. Alternatively, the one or more etalons may include anetalon wafer having a plurality of etalons.

By way of example, the substrate may include a silicon or glasssubstrate, although this is not required. An optional thermal isolationregion, such as, for example, including silicon nitride, or anotherthermally insulating material, may optionally be included in order tofurther thermally isolate the one or more etalons, although this isoptional and not required. If the substrate includes glass or otherwisesufficiently insulating material, the extra thermal isolation region isgenerally not needed.

The heating and sensing configuration includes a plurality of electricalcontacts 1290A-F, such as, for example, wire bond pads, and a pluralityof conductive pathways 1291A-F, such as, for example, metal traces. Inone or more embodiments of the invention, the electrical contacts andconductive pathways may be microfabricated as a patterned conductivemetal or other layer over the substrate, although this is not required.

In the illustrated embodiment includes a first electrical contact 1290Acoupled with a first conductive pathway 1291A, a second electricalcontact 1290B coupled with a second conductive pathway 1291B, a thirdelectrical contact 1290C coupled with a third conductive pathway 1291C,a fourth electrical contact 1290D coupled with a fourth conductivepathway 1291D, a fifth electrical contact 1290E coupled with a fifthconductive pathway 1291E, and a sixth electrical contact 1290F coupledwith a sixth conductive pathway 1291F. However, the scope of theinvention is not limited to the particular illustrated configuration.Fewer or more electrical contacts and/or leads may also optionally beincluded.

The electrical contacts may be coupled with control logic, such as, forexample, via wire bonds. The third through sixth electrical contacts1290C-F and the third through sixth conductive pathways 1291C-F may beused to monitor temperature of the etalon(s). One pair of electricalcontacts, such as, for example, electrical contacts 1290C and 1290F, maybe used to carry constant current. Another pair of electrical contacts,such as, for example, electrical contacts 1290D-E, may be used to probea voltage drop or change. The microfabricated four-wire probe may helpto isolate the RTD function from stray series resistance from wirebonding or other sources. The monitored data may be provided to thecontrol logic for purposes of calibration and/or for control ofthermo-optic tuning.

Electrical contacts 1290A and 1290B and conductive pathways 1291A and1292B may be used for temperature control or thermo-optic tuning, suchas, for example, heating and/or cooling. In one or more embodiments ofthe invention, the conductive pathways may be relatively thick, orotherwise include sufficient conductive material, such that not muchheat may be generated in these conductive pathways due to resistanceexcept in the immediate local vicinity of the one or more etalons.

Now, as discussed above, in one or more embodiments of the invention,crystalline silicon or another high index material may be included in anoptical cavity of a G-T etalon. The relatively large thermo-opticcoefficient of crystalline silicon may allow the etalon to bethermo-optically tuned tuning over a relatively small temperature range,such as, for example, of about 30° C. When tuning over such a smalltemperature range, accurate sensing of the etalon temperature may bebeneficial for operation.

Different approaches are contemplated for including temperature controldevices and temperature sensors in close proximity of the etalon inorder to promote accurate sensing and control of the temperature of theetalon. In one or more embodiments of the invention, a temperaturecontrol device, for example a resistive heater and/or thermoelectriccooler, and a temperature sensor may be coupled with the correspondingconductive pathways and positioned directly underneath or otherwiseproximate the one or more etalons. As used herein, unless specifiedotherwise, the temperature control device and temperature sensor areconsidered proximate an etalon if they are within one millimeter of atleast a portion of the etalon. In one or more embodiments of theinvention, the temperature control device and the temperature sensor mayinclude lithographically patterned metal structures, such as, forexample, of platinum or another suitable metal.

When positioned in such close proximity, the temperature control devicemay efficiently and rapidly heat and/or cool the etalon(s) and thetemperature sensor may accurately sense the temperature of theetalon(s). This may be further promoted if there is direct contact withthe etalon(s). Such close proximity and/or contact may also help toreduce the amount of power consumed to heat and/or cool the etalon(s).The optional use of a silicon optical cavity for the etalon may furtherhelp to reduce substantial thermal gradients within the etalon, sincesilicon has a relatively good thermal conductivity. This may help tobenefit accurate temperature control of the etalon(s).

As another option, in one or more embodiments of the invention, thetemperature control device and/or the temperature sensor may optionallybe monolithically integrated with the etalon substrate in order toprovide further heating efficiency and temperature sensing accuracy,although this is not required. FIG. 13 is a perspective view of a G-Tetalon 1316 having an integrated resistive heater 1394 and an integratedtemperature sensor 1393, according to one or more embodiments of theinvention. In an alternate embodiment of the invention, the G-T etalonmay optionally include an integrated thermo-electric cooler or othercooling device, or both an integrated cooling device and an integratedheating device.

The etalon may be microfabricated in an etalon substrate. The etalon hasan optical aperture 1395 that may be used to delay light of certainfrequencies, as described elsewhere herein. In one or more embodimentsof the invention, the etalon may include a single crystal siliconoptical cavity, although this is not required. The high thermalconductivity of silicon may tend to reduce thermal gradients in theetalon.

The temperature sensor may be microfabricated or otherwisemonolithically integrated optionally in close proximity of the opticalaperture. As used herein they are proximate if they are within twomillimeters. In particular, the temperature sensor may include amicrofabricated metal line or trace around at least a portion of theperiphery of the optical aperture. In one or more embodiments of theinvention, the temperature sensor may include a platinum resistivethermal device (RTD), although this is not required. Platinum may offera high coefficient of thermal resistance, good chemical stability, andis a relatively heavy element so may have good electromigrationtolerance.

In one or more embodiments of the invention, a heater-only design may beused which lacks a cooling device in favor of an ambient passive coolingmechanism. By way of example, in one or more embodiments of theinvention, the specified operating temperature range of an opticalreceiver may be from about −5° C. to 70° C. In such embodiments, thenormal operating temperature of the etalon may be about 10° C. to 40° C.higher than the maximum specified operating temperature of thetransceiver, such as, for example, about 80° C. to 110° C. This mayallow about 10° C. to 40° C. difference between normal etalon operatingtemperature and ambient, which may allow sufficient cooling to controltemperature based on only heating capability with no cooling capability.However, the scope of the invention is not so limited. For example, inan alternate embodiment, a cooling device may optionally be included toactively cool etalons, although this is not required.

XIII. Package Design

FIG. 14 is a block diagram of a top planar view of an optical receiverpackage 1460, according to one or more embodiments of the invention. Inone or more embodiments of the invention, the optical receiver packagemay include a receiver optical sub-assembly (ROSA), although the scopeof the invention is not limited in this respect.

The optical receiver package includes a port 1462, a first collimatinglens 1464, an ODC device 1402, a second collimating lens 1466, and alight detector device 1404. These components may all be housed within acommon housing of the package. In one aspect, the package may include abutterfly package, although the scope of the invention is not limited inthis respect.

The port may be capable of being optically coupled with an optical fiber1463 or other light source. In one or more embodiments of the invention,the optical fiber may include a glass single mode optical fiber,although the scope of the invention is not limited in this respect.Other optical fibers, such as, for example, plastic optical fibers andmultimode optical fibers are also potentially suitable. By way ofexample, the port may include an optical cable receptacle. Light may beprovided from the fiber or other light source to the package along anoptical path, which is shown in dashed lines.

The first collimating lens is included in the optical path. Thecollimating lens may collimate the received light. In one aspect, thecollimating lens may collimate the light to a diameter of about 300microns so that the Raleigh range is sufficient to achieve the intendeddestination, although this is not required. The first collimating lensmay focus the light on or otherwise provide the light to the ODC device.

As shown, the optical path may approach the first etalon of the ODCdevice off-axis or at a non-orthogonal angle so that reflection mayoccur from one etalon to another. When an etalon is used off axis with abeam of small diameter, the incident angle may be kept small to managebeam interference. A large angle may tend to result in “beam walk off”,which may compromise the physical overlap for interference. In one ormore embodiments of the invention, the etalons of the ODC device mayinclude crystalline silicon or another relatively high refractive indexmaterial having a refractive index greater than that of fused silicaglass in their optical path length in order to improve off-axisperformance. That is, if silicon is used for the optical path length ofthe etalons, the light may refract more strongly into the etalon and maypropagate within the etalon at a smaller angle to the normal. Thiseffect may be proportional to, or at least directly related to, theindex of refraction of the silicon. Additionally, a physically thinnerpiece of silicon may be used to achieve the same or similar opticalthickness. This effect is also proportional to or at least directlyrelated to the index of refraction of the silica. As a result, a siliconetalon with an index of about 3.4 may be tilted about 5 times furtherthan a fused silica etalon with an index of about 1.5 without furthercompromising performance. This may potentially help to avoid needing touse a beam splitter. Silicon may also similarly tolerate smaller beamdiameters.

The ODC device may have features, performance, and design featureflexibility as described elsewhere herein. The last etalon of the ODCdevice may reflect the optical dispersion compensated light to thesecond collimating lens, which is positioned in the optical path. In theillustrated embodiment, the second collimating lens is toward the frontof the package, or at the end where the light is received, although thisis not required. In an alternate embodiment of the invention, the groupsof the ODC device may optionally each have the same number of etalons sothat the optical signal may be reflected toward the back of the package.

The second collimating lens, which is optional, may help to collimatethe light on the light detector device. This may help to provide a tightfocus of light on the light detector device, which may allow a smallerand potentially less costly light detector device, although this is notrequired. The light detector device may convert the received light toone or more corresponding electrical signals that may be processed inconventional ways known in the arts.

XIII. Exemplary Optical Transceiver

FIG. 15 is a block diagram of an optical transceiver 1570, according toone or more embodiments of the invention. An optical transceiver issometimes also referred to in the arts as an optical transponder.

The optical transceiver includes an optical receiver, an opticaltransmitter 1372, control logic 1574, a physical medium attachment (PMA)device 1576, and an electrical interface 1578. These components may bephysically and/or electrically coupled with a circuit board 1580 and/orincluded within a housing.

The optical receiver and optical transmitter together form an opticalinterface 1582. By way of example, the housing may include receptaclesto receive mating terminal ends of optical cables and/or fibers. Thecables and/or fibers may communicate data in the form of optical signalsto the optical transceiver from an optical network and communicate datafrom the optical transceiver to the optical network.

In particular, the optical receiver may receive optical signals from theoptical network. The optical receiver may convert received opticalsignals to electrical signals and exchange the electrical signals withthe PMA unit. The PMA unit may exchange electrical signals with a hostdevice or other signaling medium of an electronic device in which theoptical transceiver is employed by way of the electrical interface. ThePMA unit may include various processing capabilities, such as, forexample, clock multiplier/multiplexer, and clock and datarecover/demultiplexer. The electrical interface may provide input/outputdata transfer, clocking channels, control and monitoring channels, andDC power and ground, for example. In one or more embodiments of theinvention, the optical receiver may include a receiver opticalsub-assembly (ROSA), although this is not required.

The optical transmitter may receive electrical signals from the PMA unitand may transmit corresponding optical signals to the optical network.In one or more embodiments of the invention, the optical transmitter mayinclude one or more vertical cavity surface emitting lasers (VCSELs),although other types of light sources may also optionally be used. Inone or more embodiments of the invention, the optical transmitter mayinclude a transmitter optical sub-assembly (TOSA), although this is notrequired.

As shown in the illustrated embodiment, the optical receiver may includean ODC device 1502 as disclosed herein to compensate for opticaldispersion in received light. In one or more embodiments of theinvention, an ODC device may be co-packaged with an optical receiver ina receiver optical sub-assembly package of an optical transceiver. Spaceconstraints on multi-source agreement (MSA) transceiver form factors maytend to make separately packaged ODC units undesirable. Additionally,optical receiver technology tends to be more universal in usage thanoptical transmitter technology, which may tend to be relatively moreapplication specific. For example, high performance transponders thatmay benefit from an ODC unit as described herein often use lithiumniobate modulators, which tend to be large enough to inhibitco-packaging with an ODC unit. Alternatively, in one or more embodimentsof the invention, the optical transmitter may optionally also oralternatively include an ODC device as disclosed herein. By way ofexample, the ODC device of the optical transmitter may perform opticaldispersion pre-compensation.

The control logic may include a microcontroller or analog hardware, forexample. The control logic may set control parameters of the PMA, theoptical receiver, and the optical transmitter, which may vary over time,temperature, and the like. Without limitation, to further illustratecertain concepts, specific examples of optical transceivers that aresuitable for one or more embodiments of the invention are the TXN13600optical transceivers available from Intel Corporation, of Santa Clara,Calif., although the scope of the invention is not limited to suchoptical transceivers. The TXN13600 tunable optical transceivers mayprovide long reach, such as, for example, in some cases 80 km or more,C-band and L-Band tunable 10 Gbps transceivers suitable for DenseWavelength Division Multiplexing (DWDM) network applications. By way ofexample, Intel TXN13600 optical transceivers may each include a lithiumniobate Mach-Zehnder or other modulator, microcontroller, MUX (9-bitFIFO)/DeMUX, Clock and Data Recovery (CDR) unit, jitter filter, APD andPIN receiver options, and a temperature-tuned external cavity laser,although the scope of the invention is not limited to these specificcomponents. These components may be housed within a 4.1″ L×3.5″ W×0.53″H or other form factor device, which may have relatively low powerdissipation, such as, for example, less than about 11.5 W powerdissipation. In one aspect, the device may include a 300 pin MSA module,although this is not required. The TXN13600 optical transceivers mayoptionally allow adjustment of the receiver decision threshold to allowsufficient Bit Error Rate (BER) and sufficient signal integrity. Theseare just one example of suitable optical transceivers. Other types ofoptical transceivers are also suitable.

XIV. Exemplary Network Equipment

In various embodiments of the invention, the optical transceiversdisclosed herein may be included in network equipment. Suitable types ofnetwork equipment include, but are not limited to, multi-serviceprovisioning platforms (MSPPs), optical switches, optical routers,cross-connects, optical add-drop multiplexers, and 10 Gbps/OC-192 DWDMdevices.

FIG. 16 is a block diagram of network equipment 1684 including anoptical transceiver 1670 including an ODC device 1602, according to oneor more embodiments of the invention. By way of example, the networkequipment may include a router. Alternatively, as another example, thenetwork equipment may include a switch. The switch may include switchfabric.

The network equipment includes one or more processor(s) 1686 and memory1688. Suitable processors include, but are not limited to, thosemanufactured by Intel Corporation, of Santa Clara, Calif. The opticaltransceiver, processor(s), and memory are coupled with, or otherwise incommunication with one another, by one or more buses or otherinterconnects. One type of memory used in some network equipment, butnot all network equipment, is dynamic random access memory (DRAM). Inone or more embodiments of the invention, the memory may be used tostore instructions that may be executed by the one or more processors tooperate the network equipment.

XV. Other Matters

In the description and claims, the terms “coupled” and “connected,”along with their derivatives, may be used. It should be understood thatthese terms are not intended as synonyms for each other. Rather, inparticular embodiments, “connected” may be used to indicate that two ormore elements are in direct physical or electrical contact with eachother. “Coupled” may mean that two or more elements are in directphysical or electrical contact. However, “coupled” may also mean thattwo or more elements are not in direct contact with each other, but yetstill co-operate or interact with each other, for example through anintervening component.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments of the invention. It will be apparenthowever, to one skilled in the art, that one or more other embodimentsmay be practiced without some of these specific details. The particularembodiments described are not provided to limit the invention but toillustrate it. The scope of the invention is not to be determined by thespecific examples provided above but only by the claims below.Modifications may be made to the embodiments disclosed herein, such as,for example, to the sizes, configurations, functions, materials, andmanner of operation of the components of the embodiments. All equivalentrelationships to those illustrated in the drawings and described in thespecification are encompassed within embodiments of the invention. Inother instances, well-known circuits, structures, devices, andoperations have been shown in block diagram form or without detail inorder to avoid obscuring the understanding of the description.

For clarity, in the claims, any element that does not explicitly state“means for” performing a specified function, or “step for” performing aspecified function, is not to be interpreted as a “means” or “step”clause as specified in 35 U.S.C. Section 112, Paragraph 6. Inparticular, any potential use of “step of” in the claims herein is notintended to invoke the provisions of 35 U.S.C. Section 112, Paragraph 6.

Reference throughout this specification to “one embodiment”, “anembodiment”, or “one or more embodiments”, for example, means that aparticular feature may be included in the practice of the invention.Similarly, in the description various features are sometimes groupedtogether in a single embodiment, Figure, or description thereof for thepurpose of streamlining the disclosure and aiding in the understandingof various inventive aspects. This method of disclosure, however, is notto be interpreted as reflecting an intention that the invention requiresmore features than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects may lie in less than allfeatures of a single disclosed embodiment. Thus, the claims followingthe Detailed Description are hereby expressly incorporated into thisDetailed Description, with each claim standing on its own as a separateembodiment of the invention.

Accordingly, while the invention has been thoroughly described in termsof several embodiments, those skilled in the art will recognize that theinvention is not limited to the particular embodiments described, butmay be practiced with modification and alteration within the spirit andscope of the appended claims. The description is thus to be regarded asillustrative instead of limiting.

1. An apparatus comprising: a first group of optical resonator devicesto compensate for optical dispersion by collectively delaying light, thefirst group of optical resonator devices having a first group delaycurve with a convex shape between peaks in frequency; and one or morefirst thermal devices to change the temperature of the first group ofoptical resonator devices as a group; a second group of opticalresonator devices optically coupled with the first group of opticalresonator devices to compensate for optical dispersion by collectivelydelaying light, the second group of optical resonator devices having asecond group delay curve with a concave shape at a peak in frequency;and one or more second thermal devices to change the temperature of thesecond group of optical resonator devices as a group.
 2. The apparatusof claim 1, wherein the first group of optical resonator devicescomprises optical rings.
 3. The apparatus of claim 1, wherein the firstgroup of optical resonator devices comprises Gires-Tournois (G-T)etalons.
 4. The apparatus of claim 3, wherein the G-T etalons of thefirst group are monolithically integrated on a substrate, whereinoptical cavities of the G-T etalons of the first group include differentparts of the substrate, and wherein high reflectors of the G-T etalonsof the first group share one or more layers formed over the substrate.5. The apparatus of claim 3, wherein the G-T etalons of the first grouphave the same optical path lengths and a plurality of different partialreflectivities.
 6. The apparatus of claim 3, wherein alternating G-Tetalons of the first and second groups are optically coupled in series.7. The apparatus of claim 3, wherein at least one of the G-T etalonscomprises an optical cavity including crystalline silicon.
 8. Theapparatus of claim 1, wherein a combination of the convex and concaveshapes approximates a straight line over a range of frequencies ofoptically dispersed light.
 9. The apparatus of claim 1, wherein theconvex and concave shapes comprise parabolic shapes.
 10. The apparatusof claim 1, wherein the one or more first thermal devices comprise aresistive heater that is monolithically integrated proximate an opticalresonator device of the first group.
 11. The apparatus of claim 1,further comprising a controller to control the first and second thermaldevices based, at least in part, on an error detected by receptionprocessing logic.
 12. The apparatus of claim 1, further comprising areceiver optical sub-assembly enclosing the first and second groups ofoptical resonator devices and the first and second thermal devices. 13.A system comprising: an optical dispersion compensation devicecomprising: a first group of optical devices selected fromGires-Tournois (G-T) etalons and optical ring resonators to compensatefor optical dispersion by collectively delaying light, the first groupof optical devices having a first group delay curve with a convex shapebetween peaks in frequency; and at least one first thermal device tothermo-optically tune the first group of optical devices tosubstantially the same temperature; a second group of optical devicesselected from G-T etalons and optical ring resonators optically coupledwith the first group of optical devices to compensate for opticaldispersion by collectively delaying light, the second group of opticaldevices having a second group delay curve with a concave shape at a peakin frequency; and at least one second thermal device to thermo-opticallytune the second group of optical devices to substantially the sametemperature; and a glass single-mode optical fiber to provide light tothe optical dispersion compensation device.
 14. The system of claim 13,wherein the convex and concave shapes comprise parabolic shapes.
 15. Thesystem of claim 13, wherein the optical devices of the first groupcomprise G-T etalons that are monolithically integrated on a substrate.16. The system of claim 13, wherein the optical devices of the firstgroup comprise G-T etalons that have the same optical path lengths and aplurality of different partial reflectivities.
 17. The system of claim13, wherein at least one of the optical devices of the first groupcomprises a G-T etalon having an optical cavity including crystallinesilicon.
 18. A method comprising: thermally tuning an optical dispersioncompensation device including making a convex portion of a first groupdelay curve for a first group of optical resonator devices overlap aconcave portion of a second group delay curve for a second group ofoptical resonator devices by adjusting one or more temperatures selectedfrom a temperature of the first group of optical resonator devices and atemperature of the second group of optical resonator devices; andcompensating for optical dispersion with the thermally tuned opticaldispersion compensation device.
 19. The method of claim 18, furthercomprising detecting an error in an optical signal that has been opticaldispersion compensated, and wherein said adjusting the one or moretemperatures is dependent upon the detected error.
 20. The method ofclaim 18, wherein making the convex and concave portions overlapcomprises making convex and concave parabolic portions overlap toapproximate a line.
 21. The method of claim 18, wherein said adjustingthe one or more temperatures comprises increasing a temperature of thefirst group and decreasing a temperature of the second group bysubstantially equal amounts.